This invention relates to the processing of bisphenol tars which are formed as by-products when phenols are reacted with ketones under acidic conditions, and more particularly to the recovery of useful chemical values from therefrom.
Among bisphenols prepared by the reaction of phenols with ketones under acidic conditions, bisphenol A is predominant in terms of the scale of its manufacture, its relatively low cost and the multitude of suitable applications for its use. The manufacture of bisphenol A (BPA) from acetone and phenol is practiced on a large scale with hundreds of millions of pounds of BPA produced annually. Although current processes used for its manufacture represent the fruits of years of research efforts and are highly efficient a small percentage of the starting materials are lost as a tarry by-product referred to as BPA tar. Given the scale of BPA manufacture the formation of even a small percentage of BPA tar by-product is significant and amounts to millions of pounds of tar produced annually. The tars are composed of a complex mixture of compounds which renders the separation and purification of individual components costly and inefficient. Currently employed recycle strategies for recovery of material values from BPA tars have focused on tar "cracking" in which the BPA tar is heated in the presence of an acidic or basic catalyst at atmospheric pressure. The combined action of the heat and catalyst results in bond cleavage of BPA tar components resulting in generation of phenol. The liberated phenol is distilled from the reaction vessel. The recovered phenol is then further purified and recycled into applications requiring the use of phenol.
In some instances the BPA tar has been heated in the presence of a catalyst under vacuum to afford a mixture of phenol and isopropenylphenol in the distillate. Isopropenylphenol is a valuable synthetic intermediate and its recovery from BPA tar represents an attractive means for its preparation. The recovery of both phenol and isopropenylphenol when BPA tar cracking is carried out under vacuum stands in sharp contrast to BPA tar cracking at atmospheric pressure in which little or no isopropenylphenol is obtained in the distillate. The requirement that vacuum conditions be employed for the cracking of BPA tar in order to produce a distillate containing isopropenylphenol reflects the chemical instability of isopropenylphenol and is a condition which adds cost and limits the economic viability of recovering phenol-isopropenylphenol mixtures from BPA tar.
It is of interest, therefore, to develop methods for the recovery of material values from BPA tar which do not require the use of vacuum equipment but which furnish phenol-isopropenylphenol mixtures from BPA tar under atmospheric pressure, and which will be applicable to the recovery of material values from bisphenol tars other than BPA tar.